The present invention relates to the field of advanced medical devices and particularly to intracorporeal devices for performing or aiding in the performance of therapeutic or diagnostic procedures. The intracorporeal devices may be guiding members such as guide wires for advancing intraluminal devices within various body lumens. The intracorporeal medical devices include stent delivery catheters, balloon dilatation catheters, atherectomy catheters, electrophysiology catheters and the like.
In a typical percutaneous coronary procedure, a guiding catheter having a pre-formed distal tip is percutaneously introduced into a patient's peripheral artery, e.g. femoral or brachial artery, by means of a conventional Seldinger technique and advanced therein until the distal tip of the guiding catheter is seated in the ostium of a desired coronary artery. A guide wire is first advanced by itself through the guiding catheter until the distal tip of the guide wire extends beyond the arterial location where the procedure is to be performed. Then a rapid exchange type catheter, such as described in U.S. Pat. No. 5,061,273 (Yock) whose contents are hereby incorporated by reference, is mounted onto the proximal portion of the guide wire which extends out of the proximal end of the guiding catheter outside of the patient. The catheter is advanced over the guide wire, while the position of the guide wire is fixed, until the operative element on the rapid exchange type catheter is disposed within the arterial location where the procedure is to be performed. After the procedure is performed, the rapid exchange type catheter may be withdrawn from the patient over the guide wire, or the guide wire may be repositioned within the coronary anatomy for an additional procedure. Of course, the procedure may also be performed with an over-the-wire (OTW) type catheter and is not limited to just rapid exchange (RX) type catheters.
A guide wire may also be used in conjunction with the delivery of an intravascular stent. One method and system involves disposing a compressed or otherwise small diameter stent over an expandable member, such as a balloon, at the distal end of a catheter. The physician advances the catheter through the patient's vascular system over a guide wire until the stent is at the desired location within a blood vessel. The expandable member on the catheter is inflated to expand the stent within the blood vessel. The dilated expandable member is then deflated and the catheter withdrawn, leaving the expanded stent within the blood vessel. Once deployed, the expandable member ensures patency of the blood vessel by holding the passageway open. This latter method and system can be used concurrently with balloon angioplasty or subsequent thereto.
Further details of guide wires and devices associated therewith for various interventional procedures can be found in, for example, U.S. Pat. No. 4,748,986 (Morrison et al.); U.S. Pat. No. 4,538,622 (Samson et al.); U.S. Pat. No. 5,135,503 (Abrams); U.S. Pat. No. 5,341,818 (Abrams et al.); and U.S. Pat. No. 5,345,945 (Hodgson, et al.), whose contents are hereby incorporated by reference.
Conventional guide wires for angioplasty, stent delivery, atherectomy, and other intravascular procedures usually have an elongate core with one or more segments near the distal end thereof that taper distally to smaller cross-sections. A flexible body, such as a helical coil or a tubular body of polymeric material, is typically disposed about and secured to at least part of the distal portion of the core. A shapeable tip, which may be the distal extremity of the core or a separate shapeable ribbon that is secured to the distal extremity of the core, extends through the flexible body and is secured to the distal end of the flexible body by soldering, brazing, or welding; or by use of an adhesive in the case of a polymeric flexible body which forms a rounded distal tip or tip ball. This rounded, distal or leading tip is highly flexible so that it does not damage or perforate the vessel. The portion behind the distal tip is increasingly stiff to better support a balloon catheter or similar device.
The shapeable member or ribbon of a typical guide wire is a small diameter wire that has been flattened to a relatively constant transverse profile. Flattening of the shapeable member facilitates the shapeability of the member. However, a shapeable member having a constant transverse profile or flexibility could be subject to prolapse during use. Prolapse occurs when the shapeable member gets bent back on itself inside a constrained lumen, and is difficult to straighten out with only proximal manipulation.
Some guide wires have been formed from a pseudoelastic, shape memory alloy such as nitinol (i.e., nickel-titanium or NiTi) to achieve both flexibility and strength. When stress is applied to nitinol alloy exhibiting pseudoelastic characteristics at a temperature at or above the transformation of martensite to austenite is complete, the material deforms elastically until it reaches a particular stress level where the alloy then undergoes stress-induced phase transformation from austenite back to martensite. As the phase transformation proceeds, the alloy undergoes significant increases in strain but with little or no corresponding increases in applied stress. In other words, the strain increases while the stress applied remains essentially constant until the transformation of the austenite to the martensite is complete. The martensite that appears under this type of loading is commonly called stress induced martensite (SIM). Thereafter, further increases in stress are necessary to cause more deformation in the material.
If the load on the nitinol alloy is removed before any permanent deformation has occurred, the martensite in the material elastically recovers and transforms back to austenite. The gradual reduction in stress first causes a decrease in strain. As stress reduction reaches the level at which the martensite transforms back to the austenite, the stress level in the material remains again essentially constant until the transformation back to austenite is complete. That is, there is significant recovery in strain with only negligible corresponding stress reduction. After the transformation back to austenite is complete, further stress reduction results in elastic strain reduction. This ability to incur significant strain at relatively constant stress upon the application of a load and to recover from the deformation upon the removal of the load is commonly referred to as pseudoelasticity. These properties to a large degree allow a guide wire core of a pseudoelastic material to have both flexibility and strength. The term “pseudoelasticity” is sometimes used interchangeably with “superelasticity.”
While the properties of the guide wires formed from pseudoelastic or superelastic material were very advantageous, it was found that some of the guide wires and guiding members formed from such materials did not have optimal push and torque transmission characteristics.